1. Field of the Invention.
The present invention relates to a resistance measurement device, and more particularly, to an apparatus for measuring the electrical resistance of a test specimen.
2. Description of the Related Art.
When measuring the resistance of a test specimen, such as a conductor of a printed circuit board, it is known that inaccuracies arise since the semiconductor switches for triggering the conductor are not ideal switches. More specifically, a residual current flows via a parallel resistance when the semiconductor switch is open, whereas a voltage drop results at a series resistance when the semiconductor switch is closed. Accordingly, when the semiconductor switch is closed (i.e., when an electrical connection is made to the test-specimen), the voltage drop at the series resistance results in inaccuracies in the resistance measurement.
Accordingly, in an effort to obviate the above-noted inaccuracies in the resistance measurement, it is known to measure the resistance of a test specimen according to the "Kelvin Method" . According to this method, as shown in FIG. 1, electrical connection to the test-specimen 7 is effected via two parallel connected semiconductor switches 1, 2. A test current I.sub.p is applied to the test-specimen 7 via semiconductor switch 1 and its associated resistor 3. The voltage drop across resistor 3 is measured by the voltage-measuring device 12 which is connected in series with the semiconductor switch 2. To effect the resistance measurement, the semiconductor switch 1 and the semiconductor switch 2 are closed simultaneously.
According to this method, the voltage drop appearing across resistor 3 up to node 5 is compensated for in the resistance measurement. As shown in FIG. 1, the test-specimen 7 is a portion of a conductor of a printed circuit board 8, and the resistance measurement is effected between test probes 9 and 10. Reference numeral 11 denotes a current measurement device for measuring the current flowing through the test-specimen.